There are a wide range of contexts in which it is necessary to determine the position of a remote object. One particularly difficult context is in tracking the positions of individual leaves of a multi leaf collimator (MLC) in a linear accelerator (Linac). An MLC is used to shape the beam of X-ray (or other) radiation produced by a linac, in order to treat a patient. For the control system to deliver a correctly shaped dose, the position of each leaf must be accurately determined. Current methods that are employed use a combination of a standard CCTV camera and reflectors positioned on each leaf. A source of light illuminates the area in which the reflectors lie, and the CCTV camera receives an image that includes the reflections. The position of each leaf can then be determined from the position of each reflection within the CCTV camera image.
The main problem with such systems is that the accuracy and resolution are limited by the number of pixels within the camera. This cannot be easily increased. In addition, most electronics (including CCTV cameras) are susceptible to radiation, and will eventually break down if exposed to significant levels. Radiation hardened cameras can be designed, but these are expensive and are usually bespoke, so are not readily available.
Most CCTV cameras also have a limited frame rate of (typically) 30 frames per second at most. Where fast movements are required of the MLC leaves, this frame rate may not be adequate to keep up.
Video processing software is also required, which is computationally demanding and therefore increases system complexity and cost.
The CCTV camera is bulky, and needs to be fitted into an area where space is at a premium.
Electromagnetic noise generated from within the Linac can interfere with the image quality and may interfere with the image processing software, causing a loss of leaf positions.
Other contexts exist in which similar problems are encountered, however.
Finally, CCTV cameras are responsive to a broad range of optical wavelengths, making them susceptible to sources of interference such as room lasers, fluorescent lights, and the like.